I have been palying since August 2001 and this is the first time I have seen this.
I was invited to a team the same time as another person....I guess I didn't react fast enough, so they invited another person. Well we both must of clicked OK at the same time because now we were the #6 and #7 team members. With the other guy at #7 clearly showing on the team list, with HP and NP bars. We were able to pull a mish and run it without any problems.
Weird.